1. Field of the Invention
The present invention relates in general to the recording and playback of a digital video cassette recorder (VCR), and more particularly to a recording/playback apparatus for a digital VCR that prevents a degradation in a picture quality when playing back compressed video data of sequential programs edited, recorded on a single digital storage media (DSM) or when the digital VCR begins a playback operation again after being stopped.
2. Description of the Prior Art
Referring to FIG. 1, there is shown a block diagram of a conventional recording/playback apparatus for a digital VCR. As shown in this drawing, the conventional recording/playback apparatus comprises a formatter 1 for converting a format of compressed video data inputted therein into a recording format of a magnetic tape T, an error correction coder 2 for performing an error correction coding operation for output data from the formatter 1 to prevent it from being mixed with an error, a channel modulator 3 for modulating output data from the error correction coder 2 suitably to a channel characteristic of the magnetic tape T, and a recording amplifier 4 for amplifying output data from the channel modulator 3 so that it can be recorded on the magnetic tape T and output to a recording bead HD1.
The conventional recording/playback apparatus also comprises a playback amplifier 5 for amplifying by a predetermined level the compressed video data which is detected from the magnetic tape T by a playback head HD2, a channel demodulator 6 for demodulating output data from the playback amplifier 5, an error correction decoder 7 for performing an error correction decoding operation for output data from the channel demodulator 6 to correct an error mixed therewith in recording and playback processes, and a deformatter 8 for converting a format of output data from the error correction decoder 7 into the format of the original compressed video data.
The operation of the conventional recording/playback apparatus with the above-mentioned construction will hereinafter be described with reference to FIGS. 2 and 3. FIG. 2 is a view illustrating a conventional manner of compressing high definition television (HDTV) video data and FIG. 3 is a view illustrating a conventional manner of playing back the video data compressed by the conventional manner of FIG. 2 with two programs edited and recorded on the magnetic tape.
As shown in FIG. 2, the HDTV video data of one picture is compressed by an intraframe coding (dashed region) and an interframe coding (non-dashed region). For the purpose of preventing an error generated in a certain picture from having an effect on the subsequent pictures, the intraframe coding is performed cyclically on left, middle and right sides of the pictures at an interval of three pictures.
Upon inputting the HDTV video data compressed in the above manner, the formatter 1 converts the format of the inputted video data into the recording format of the magnetic tape T. The error correction coder 2 performs the error correction coding operation for the output data from the formatter 1 to prevent it from being mixed with an error. The channel modulator 3 modulates the output data from the error correction coder 2 suitably to the channel characteristic of the magnetic tape T. The recording amplifier 4 amplifies the output data from the channel modulator 3 so that it can be recorded on the magnetic tape T and outputs the amplified data to the recording head HD1. Then, the output data from the recording amplifier 4 is recorded on the magnetic tape T by the recording head HD1.
For the playback of the compressed video data recorded on the magnetic tape T in the above manner, the compressed video data is detected from the magnetic tape T by the playback head HD2 and then applied to the playback amplifier 5, which amplifies the detected video data by the predetermined level. The channel demodulator 6 demodulates the output data from the playback amplifier 5. The error correction decoder 7 performs the error correction decoding operation for the output data from the channel demodulator 6 to correct an error mixed therewith in the recording and playback processes. The deformatter 8 converts the format of the output data from the error correction decoder 7 into the original format of the compressed video data.
However, in the case where the compressed video data with a plurality of programs (for example, two programs) are edited, recorded on the magnetic tape and played back as shown in FIG. 3, an interframe coded region (non-dashed region) of a start picture (picture 3) of the program 2 is played back on the basis of a last picture (picture 2) of the program 1, resulting in degradation in a picture quality. Such a degradation may be extended at the maximum to six of the pictures of the video data compressed as shown in FIG. 2. Also, the number of degraded pictures increases in number as an intraframe coded region is made narrower.